The present invention relates to a method and apparatus for predicting the properties of a polymer latex in an emulsion polymerization process and more particularly relates to a method and apparatus of using the predicted polymer latex properties to monitor and adjust the process parameters of an emulsion polymerization process to improve the quality and productivity of the process and the emulsion polymer latices produced therefrom.
One common method for producing polymers such as homopolymers and copolymers is emulsion polymerization. In a typical emulsion polymerization process, monomers are combined with an initiator in the presence of a surfactant in an aqueous medium and the monomers are polymerized to form the polymer. For example, the monomers can be combined with a surfactant and water to form a pre-emulsion and the pre-emulsion and initiator separately fed to a reactor where the polymerization reaction occurs to form the polymer. Alternatively, the monomers, an aqueous surfactant solution and an initiator can each be fed separately to the reactor.
It is important that the polymer latices produced in the emulsion polymerization process are consistent and of good quality. To ensure acceptable product quality, it has traditionally been necessary to take samples of the polymer latex at various stages or times during the emulsion polymerization process. Analytical tests are then conducted on the samples to verify that the samples are of sufficient quality. If the analytical tests do not produce values within certain specified limits, the process is modified to alter the product such that the product is of sufficient quality.
One drawback to the traditional method of process quality control is that it takes time to receive the results from the analytical tests. Accordingly, the emulsion polymerization process must be delayed resulting in reduced production. In addition, the sampling and testing is retrospective and does not allow the process to be proactively controlled. Furthermore, taking and analyzing samples can be expensive. Therefore, there is a need to provide a method of proactively controlling an emulsion polymerization process that produces a quality product without reducing the amount of the latex polymer produced and without increasing the cost of the process.
The present invention provides a method for predicting polymer latex properties for an emulsion polymer latex based on statistical relationships between the polymer latex properties and process parameters. The method of the invention allows for real-time control of the emulsion polymerization process and thus facilitates the production of a quality emulsion polymer without the need to stop production for sampling and analytical testing. The method of the invention also provides feedback and feed forward control of the emulsion polymerization process to ensure the production of a quality product without increasing the cost of production. Furthermore, the statistical relationships between the polymer latex properties and process parameters determined for a specific emulsion polymerization process can advantageously be used to predict the polymer latex properties for another emulsion polymerization process making generally the same polymer. The method of the invention can be used with continuous, batch and semi-batch emulsion polymerization processes.
The method for predicting one or more polymer latex properties for an emulsion polymer latex according to the invention includes conducting an emulsion polymerization process in a reactor including one or more reactor inputs to produce an emulsion polymer latex, measuring a set of process parameters for the emulsion polymerization process, performing a heat balance and a mass balance across the reactor based on the set of measured process parameters to determine a set of calculated polymer latex properties for the emulsion polymerization process, and determining one or more predicted polymer latex properties for the emulsion polymer latex being prepared in the emulsion polymerization process using process parameters selected from one or more of said set and said second set and a predetermined set of statistical relationships between the selected process parameters and the polymer latex properties to be predicted. The heat balance and mass balance are typically conducted using a set of measured process parameters including the mass of ingredients initially added to the reactor, the flow rates for the reactor inputs, the temperatures for the reactor inputs, the flow rates and temperatures for the input and output of a coolant stream communicating with the reactor, and the temperature and pressure of the reactor, to determine a set of calculated process parameters such as the monomer/polymer ratio in the reactor. The one or more predicted polymer latex properties for the emulsion polymer are preferably determined using the reactor temperature, the flow rates for the reactor inputs, the monomer/polymer ratio and a predetermined set of statistical relationships between the reactor temperature, the flow rates for the reactor inputs, the monomer/polymer ratio and the polymer latex properties to be predicted.
In accordance with the invention, the set of statistical relationships between the process parameters and the polymer latex properties used are preferably determined by first operating the emulsion polymerization process using a plurality of varying process parameters and measuring the polymer latex properties and then calculating the set of statistical relationships between the process parameters and polymer latex properties for the emulsion polymerization process based on the process parameters and the measured polymer latex properties. In addition to the measured polymer latex properties, polymer latex properties such as the monomer/polymer ratio calculated by performing a heat balance and mass balance across the system can be used to determine the statistical relationships. Preferably, the process parameters used to provide the set of statistical relationships are selected from the group consisting of the reactor temperature and the flow rates for the reactor inputs. In addition, the measured and calculated polymer latex properties are preferably selected from the group consisting of the monomer/polymer ratio, the number of polymer particles, the amount of polymer crosslinking, the molecular weight of the polymer, the concentration of Diels-Alder adducts and the polymer particle size. Preferably, the monomer/polymer ratio, the flow rates for the reactor inputs, the reactor temperature, and the statistical relationships are used to predict polymer latex properties such as the number of polymer particles, the amount of polymer crosslinking, the molecular weight of the polymer, the concentration of Diels-Alder adducts and the polymer particle size.
The predicted polymer latex properties can be used in various ways to provide a more consistent emulsion polymer product. For example, the predicted polymer latex properties can be compared to predetermined upper and lower limits for the polymer latex properties. If the predicted polymer latex properties are not within the predetermined upper and lower limits for the polymer latex properties, a sample of the emulsion polymer from the emulsion polymerization reaction can be taken and the actual polymer latex properties from the sample measured to determine if the process parameters for the emulsion polymerization reaction should be adjusted. Alternatively, the process parameters for the reactor or for further processing steps downstream from the reactor can be adjusted if the predicted polymer latex properties are not within the predetermined upper and lower limits for the polymer latex properties to provide feedback or feed forward control. The predicted polymer latex properties can also be analyzed using statistical process control methods to determine whether the predicted polymer latex properties are acceptable and whether process parameters for the emulsion polymerization process or for further processing steps downstream from the reactor need to be adjusted. The processing steps downstream from the reactor can include at least one of a redox treatment step, a steam stripping step and an agglomeration step and the process parameters that can be adjusted include the amount of redox chemicals in the redox treatment step, the addition time for the redox treatment step, the amount of steam in the stripping step, the stripping time in the steam stripping step, the temperature of the steam stripping step, and the pressure in the agglomeration step.
The present invention also includes an apparatus for predicting the polymer latex properties of an emulsion polymer latex using the process parameters for the emulsion polymerization reaction. The apparatus includes a reactor including one or more reactor inputs for producing an emulsion polymer latex, means for measuring a set of process parameters for the emulsion polymerization process communicating with the reactor, means for performing a heat balance and a mass balance across the reactor based on the set of process parameters to determine a set of calculated polymer latex properties for the emulsion polymerization process, the performing means communicating with the measuring means, and means for determining one or more predicted polymer latex properties for the emulsion polymer being prepared in the emulsion polymerization process using process parameters selected from one or more of the set and the second set and a predetermined set of statistical relationships between the selected process parameters and the polymer latex properties, the determining means communicating with the measuring means and the performing means. Preferably, the reactor further includes a coolant stream and said measuring means measures a set of process parameters that includes the mass of ingredients initially added to the reactor, the flow rates for the reactor inputs, the temperatures for the reactor inputs, the flow rate and temperatures for the coolant stream input and output, and the temperature and pressure of the reactor. In addition, the means for performing a heat balance and a mass balance across the reactor based on the set of process parameters is preferably used to determine the monomer/polymer ratio in the reactor. The determining means preferably determines one or more predicted polymer latex properties for the emulsion polymer using the reactor temperature, the flow rates for the reactor inputs, the monomer/polymer ratio and a predetermined set of statistical relationships between the reactor temperature, the flow rates for the reactor inputs, the monomer/polymer ratio and the polymer latex properties to be predicted.
In addition to the above, the apparatus also preferably includes means for measuring polymer latex properties for the emulsion polymerization process and means for calculating the set of statistical relationships between the process parameters and polymer latex properties for the emulsion polymerization process based on the measured process parameters and measured and calculated polymer latex properties, the calculating means communicating with the means for measuring a set of process parameters, the means for measuring polymer latex properties, the performing means and the determining means, wherein the determining means uses the statistical relationships calculated by the calculating means to determine the one or more predicted polymer latex properties. The means for measuring a set of process parameters can measure process parameters selected from the group consisting of the reactor temperature and the flow rates for the reactor inputs. The means for measuring polymer latex properties can measure polymer latex properties selected from the group consisting of the monomer/polymer ratio, the number of polymer particles, the amount of polymer crosslinking, the molecular weight of the polymer, the concentration of Diels-Alder adducts and the polymer particle size. The performing means typically calculates the monomer/polymer ratio for the reactor. The determining means preferably uses the monomer/polymer ratio, the flow rates for the reactor inputs, the reactor temperature, and the statistical relationships from the calculating means to determine predicted polymer latex properties selected from the group consisting of the number of polymer particles, the amount of polymer crosslinking, the molecular weight of the polymer, the concentration of Diels-Alder adducts and the polymer particle size.
In a preferred embodiment of the invention, the apparatus further includes means for comparing the predicted polymer latex properties to predetermined upper and lower limits for the polymer latex properties. The apparatus can then further include means for adjusting the process parameters for the reactor if the predicted polymer latex properties are not within predetermined upper and lower limits for the polymer latex properties. Alternatively, the apparatus can include one or more additional processing stages such as those described above for the emulsion polymerization process downstream from said reactor and means for adjusting the process parameters for the additional processing stages if the predicted polymer latex properties are not within predetermined upper and lower limits for the polymer latex properties. The apparatus can further include statistical process control means for analyzing the predicted polymer latex properties to determine whether the predicted polymer latex properties are acceptable and means for adjusting the process parameters for the emulsion polymerization process if the predicted polymer latex properties are not acceptable. Alternatively, if the apparatus includes an additional processing stage as discussed above, the statistical process control means can analyze the predicted polymer latex properties to determine whether the predicted polymer latex properties are acceptable and the apparatus can include means for adjusting the process parameters for the additional processing stages.
In an alternative embodiment of the invention, the apparatus for predicting the properties of a polymer latex formed by an emulsion polymerization process includes first processing means for performing a heat balance and a mass balance for a reactor including one or more reactor inputs in an emulsion polymerization process to determine a set of calculated polymer latex properties for the emulsion polymerization process based on a set of measured process parameters and second processing means communicating with the first processing means for determining one or more predicted properties for the polymer latex using the calculated polymer latex properties determined by the first processing means, the set of measured process parameters, and a set of predetermined statistical relationships between the process parameters and the polymer latex properties to be predicted. In addition, the apparatus can include processing means communicating with the first processing means for analyzing the actual properties for a polymer latex and the process parameters for the emulsion polymerization process to determine statistical relationships between the polymer latex properties and the process parameters for use in determining the predicted polymer latex properties. The apparatus can also include processing means communicating with the second processing means for comparing the predicted polymer latex properties to predetermined upper and lower limits. The apparatus can also include a control system for adjusting process parameters for the reactor or for processing steps downstream of the reactor if the predicted polymer latex properties are not within the predetermined upper and lower limits for the polymer latex properties. The apparatus can also include processing means for analyzing the calculated polymer latex properties determined by the first processing means, the set of measured process parameters, and the predicted polymer latex properties determined by the second processing means to determine if the predicted polymer latex properties are acceptable and if the process parameters for the reactor or for processing steps downstream from the reactor need to be adjusted.
The present invention also further includes a computer program product for predicting the properties of an emulsion polymer latex that includes a computer-readable storage medium having computer readable program code means embodied in the medium. The computer-readable program code means includes first computer instruction means for performing a heat balance and a mass balance across a reactor for an emulsion polymerization process to determine a set of calculated polymer latex properties for the emulsion polymerization process using a set of measured process parameters and second computer instruction means for determining one or more predicted polymer latex properties for the emulsion polymer latex being prepared in the emulsion polymerization process using the set of calculated polymer latex properties, the set of measured process parameters, and a set of predetermined statistical relationships between the calculated process parameters, the measured process parameters and the polymer latex properties to be predicted. The computer program product preferably also includes instruction means for determining the set of statistical relationships between the process parameters and polymer latex properties used by the second computer instruction means based on a plurality of varying process parameters for the emulsion polymerization process and polymer latex properties measured from the emulsion polymerization process. The computer program can also include computer instruction means for comparing the predicted polymer latex properties to predetermined upper and lower limits for the polymer latex properties. Furthermore, the computer program product can include computer instruction means for analyzing the set of calculated process parameters, the set of measured process parameters and the predicted polymer latex properties using statistical process control methods to determine if the predicted polymer latex properties are acceptable and if the process parameters for the emulsion polymerization process or for processing steps downstream of the emulsion polymerization process need to be adjusted.
These and other features and advantages of the present invention will become more readily apparent to those skilled in the art upon consideration of the following detailed description and accompanying drawings, which describe both the preferred and alternative embodiments of the present invention.